RE: Re: Whoooosh..thud..oh bugger

["Paul Gale" <groups2@xxxxxxxxxxxxxxxx>]

Any pictures yet?

Would be interesting to see...

Paul.


> -----Original Message-----
> From: ukha_d@xxxxxxx [mailto:ukha_d@xxxxxxx] On Behalf
> Of Martin Howell
> Sent: 11 April 2007 17:56
> To: ukha_d@xxxxxxx
> Subject: Re: [ukha_d] Re: Whoooosh..thud..oh bugger
>
> Thanks Simon, not as strange a suggestion as it might seem.
>   I originally planned a fully automated system, using a
> controller devised by Rodney Hall (on this list, thanks
> Rodney), but decided against it on the grounds that it would
> be pretty complex - IR beams to trigger both open and close;
> obstruction detection; manual overrides etc - and that it
> would need too many fail-safes to stop it from squashing
> people, and avoid getting Aunt Edna getting trapped in the
> lounge for several days while we worked out what had gone wrong.
>
> I'm sticking with the simple manual approach for now, with a
> series of micro switches to slow the door down for the last
> 6 inches of travel and to shut the power off before the door
> hits the stops, together with some cushioning of the cable
> drive mechanism.  As a last resort (and with higher WAF), I
> could disconnect the drive completely and just add a handle
> on both sides, though there's still the problem of small
> boys closing the door enthusiastically and forgetting to
> move all their body parts out of the way...
>
> Martin
>
> Simon Pawson wrote:
> > I tried this reply last night but haven't seen it yet...
> >
> > Coming totally from a strange direction....
> >
> > could you do something with a reversing sensor system for a car.
The
> bar
> > graph of LEDS could be converted to opto-isolators driving relays
> with
> > build in resistors to slow the travel.
> >
> > Might be hard getting a reliable bounce if wall/frame mounted.
Easier
> > spotting the wall from the door but not so elegant. Could be set
up
> as a
> > safety measure as well. Child in the way stops (or even beeps).
> >
> > Sorry just an odd thought - back to the merlot.
> >
> > Simon
> >
> >
> > In message <461A91D0.8000200@xxxxxxx>, Martin Howell
> > <martin.howell@xxxxxxx> writes
> >> Hmm, this unit from RS gives the 'soft start' I'm looking
> >> for, but not the 'soft stop, which is where the real problem
> >>  lies.  I agree with your analysis of the drive train
> >> issues, but I'm concerned that strengthening the cables and
> >> applying more tension will just move the force to the next
> >> weakest part of the drive - the cable fails at present
> >> because of a joint, inserted partly to prevent breaking a
> >> more difficult to fix part of the drive.  I'm looking at a
> >> more simplistic system of forcing a slow down at each end of
> >> the movement, watch this space to see if it works, or if the
> >> whole contraption bursts through the wall into the garden :-)
> >>
> >> Martin
> >>
> >> David Cole wrote:
> >>> Martin
> >>>
> >>> Sounds to me like you need a PWM (Pulse Width Modulation)
drive to
> >>> efficiently control the speed of the motor.
> >>>
> >>> Something along the lines of 510-1209 at RS should do it,
this
> would
> >>> give the acceleration and deceleration whilst also
limiting the
> >>> current if the door jammed. Alternatively google for PWM
DC drive
> >>> circuit
> >>>
> >>> You want to ensure that your drive train (cables) are as
stiff as
> >>> possible, this is why industrial applications usually use
rack and
> >>> pinion drives. This may mean increasing the diameter of
the cable
> to
> >>> ensure that you don't have any stretch which causes jerk.
It sounds
> >>> like you have a lot of inertia in your system it may help
if you
> add
> >>> additional gearing which will reduce the speed, increase
the torque
> >>> but also decrease the amount of reflected inertia seen by
the
> motor.
> >>>
> >>> Hope this helps
> >>>
> >>> Regards
> >>>
> >>> Dave
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >>>
> >> --
> >>
> >>
> >> Grizelli Associates Limited
> >> IT Project Consultants
> >> 2c Nethermoor Road, Middlezoy, Bridgwater, TA7 0PG
> >> UK Company registration no. 2468872
> >> VAT registration no. 713 1775 49
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >
>
> --
>
>
> Grizelli Associates Limited
> IT Project Consultants
> 2c Nethermoor Road, Middlezoy, Bridgwater, TA7 0PG
> UK Company registration no. 2468872
> VAT registration no. 713 1775 49
>
>
>
>
>
>